Daredevil Nik Wallenda has become the first person to walk across Niagara Falls on a high wire.

Tens of thousands of people gathered at the falls and millions more were believed watching on television as Wallenda crossed some 200 feet in the air on a two-inch-wide wire strung over the raging waters of Horseshoe Falls, the largest of the three falls that make up Niagara Falls.

Others have crossed the Niagara River itself, but never over the falls. Wallenda said that tonight's feat will be the fulfillment of a lifelong dream as well as a chance to honor his great-grandfather, legendary funambilist Karl Wallenda, who died after falling from a tightrope in Puerto Rico in 1978.

Wallenda, 33, has called his great-grandfather his "biggest inspiration" and said he will be thinking of him during the stunt. The 1,500-foot walk between Goat Island in the U.S. side to Table Rock in Canada will be fraught with unforgiving natural conditions: blinding mist and drafts created by the force of the waterfalls crashing down on the Niagara River.

Those obstacles notwithstanding, Wallenda told reporters Thursday that he hopes the walk will be "peaceful and relaxing."

"Often, I'm very relaxed when I'm walking on a cable like that," he said, but he added that the historic nature of the event could also mean "there'll be some tears involved."

Preparing for the walk took months. In addition to actually practicing for the walk, Wallenda had to secure permission from both U.S. and Canadian authorities. On the Canadian side, giving Wallenda the go-ahead meant granting a one-time exemption on a 128-year ban on stunts. Wallenda's team also had to devise and implement measures to steady the wire and guarantee that, should Wallenda stumble, safety equipment would keep him from plunging down into the gorge.

Today, in the hours before the walk, Wallenda planned to focus his energy on friends and family.

"I have lot of friends that I haven't seen for a while that have all flown in to be here for this event, so I'm going to spend some time with them and hang out," he said on "Good Morning America" today.

At least one person close to Wallenda will not be at Niagara Falls to watch the event. Wallenda told "Good Morning America" that his grandmother couldn't be there, but that he promised her that he would call her as soon as he made it to Table Rock.

Tonight's event is expected to bring a major boost to tourism in the Niagara Falls region, which sees 13 million visitors at the falls each year.

"Over a billion people by Monday will have known the story of Nik Wallenda over Niagara Falls," Tim Clark, of the Buffalo-Niagara Film Board, told ABC News affiliate WKBW, "and I think that's just fantastic reinforcement for our tourism industry here in western New York."